The invention relates to a sampling process or a sampling technology and to a sampling apparatus which belongs to the process and will be referred to herein below, for short, as a sampler.
Sampling is the removal of a sample in accordance with a defined process. This serves the purpose of making reliable statements relating to the quality, nature or composition of a certain material. The procedure of removing the material brings forth a sample.
Great interest is attached to so-called “in-situ” sampling, which is becoming more important in present times and which energy and raw-materials companies use for exploring deposits or reservoirs, usually prior to the latter being developed. The expression so-called “in-situ” sampling means, in the branch of geological science relating to this patent application, sampling “on site” while maintaining essential environmental variables, in particular the main parameters of pressure and temperature. Importance is placed here not just on maintaining the parameters, but also on obtaining an intact sample with minimal contamination.
Conventional sampling techniques which are known at present lack accurate renderings of the true actual values of the sample. This is reported in [Anders, Erik: Theorie and Praxis der “in-situ” Probenahme in der maritimen Technik [theory and practice of maritime “in-situ” sampling], Dissertation at the Technical University of Berlin, 2009] and [Paull C. K., Ussler III W. (2000): “History and significance of gas sampling during DSDP and ODP drilling associated with gas hydrates” In: Paull, C. K., Dillon, W P. (Eds.), Natural Gas Hydrates: Occurrence, Distribution and Detection. Am. Geophys. Union, Washington, D.C., pp. 53-65] and also [Wallace P. J., Dickens G. R., Paull C. K., Ussler W. III (2000): “Effects of core retrieval and degassing on the carbon isotope composition of methane in gas hydrate- and free gas-bearing sediments from the Blake Ridge” In: Paull, C. K., Matsumoto, R., Wallace, P. J., and Dillon, W. P. (Eds), Proc. ODP, Sci. Results, 164: College Station, Tex. (Ocean Drilling Program), 101-112. doi: 10.2973/odp.procs.sr.164.209.2000]. According to these reports, the samples undergo irreversible changes during the recovery periods, and are subject to the fundamental influence of vastly altered environmental conditions, and therefore a large number of biochemically and physically conditioned processes are exposed to irrevocable alterations and are therefore unusable for some research, as is reported in [Waite W. F., (2008): “Physical property changes in hydrate-bearing sediment due to depressurization and subsequent repressurization” Lawrence Berkeley National Laboratory (University of California, University of California), Year 2008 Paper LBNL-664E].
It is precisely in the field of new technologies that there is a major need for accurate information relating to a deposit, the conventional methods being insufficient, or unable, to provide this information. An example of such new technologies is constituted by the recovery of gases from coal-seam deposits or from low-permeability deposits or the recovery of gas hydrates for example methane hydrate.
Information relating to the construction or the composition of a geological formation is, for example, also required in preliminary investigations of potential reservoirs for storing CO2.
[Abegg F., Hohnberg H.-J., Pape T., Bohrmann G., Freitag J. (2008): “Development and application of pressure-core-sampling systems for the investigation of gas- and gas-hydrate-bearing sediments” Deep Sea research Part I: Oceanographic Research Papers, Deep-Sea research I 55: 1590-1599] describes, for example, how to investigate highly unstable gas hydrates, which quickly decompose under changes in pressure and temperature.
So-called “autoclave samplers” are used here for recovering and investigating soil samples while maintaining the prevailing “in-situ” conditions. The term “autoclave” relates to its literal meaning and refers to the “self-closing” operation of the sampler on site. The “self-closing” operation on site serves for conserving the environmental conditions present, that is to say the “in-situ” conditions. The term “autoclave” here does not relate to the effect of sterilization, as is used in conventional medical/biological applications.
“Autoclave samplers” always follow the same principle: the sampler is positioned at a promising location and extracts the desired sample. The latter is then closed in a pressure-tight and thermally insulated manner on site and then recovered. The essential part of this sequence is the operation of raising the recovered sample material into a pressure chamber, past a lower closure mechanism. The following closure of the autoclave sampler ensures that the environmental conditions prevailing there—“in situ”—are maintained. Such autoclave samplers, in the broadest sense, are disclosed in DE 10 2008 047 905 A1, DE 103 46 351 B2, GB 2 05009 A, GB 2 000 824 A, CN 201 723190 U, U.S. Pat. No. 5,482,123 A, U.S. Pat. No. 6,216,804 B1 and US 2002/0033281 A1.
A sampling technology which is currently used in deep drilling makes use of autoclave samplers which are capable of self-closing at the sample-extraction site, and therefore the environmental conditions present on site, in particular pressure and temperature parameters, can be conserved until investigation of the sample takes place or investigation of the sample has been completed. This sampling technology is the so-called “wire-line process”. An autoclave sampler here is let down within the drill string and docks in the lower part of the drill string [Bottom Hole Assembly], directly above the drill bit. Following sampling and the operation of raising the sample into a pressure chamber of the autoclave sampler, the sampler is recovered again with the aid of a long cable. Disadvantages of this process, however, are constituted by the dimensions of the pressure sampler, which are very limited by the drill string, and, for example, the small core diameter of the sample which is the result of using a sampler-closing ball valve which takes up a lot of space. The autoclave sampler with such a ball valve and also the associated “wire-line process” are described, for example, in U.S. Pat. No. 4,317,490 A.
So-called “rotary drilling”, which has been known for some time now, is used for deep-drilling purposes. The process is distinguished essentially in that a drill hole having a drill-hole floor is drilled. The main element for carrying out the process is formed here by a drill string, which extends from a surface to the lowermost location of the drill hole and, despite a comparatively small overall diameter of 10 to 20 cm, may be a number of kilometers in length. The drill string is subdivided into a multiplicity of sub-segments and is sunk down from the drill rig. The drill string is usually driven from the drill rig, from where it is moved both in translatory and in rotary fashion. Advancing movement and rotational drilling speed are realized and regulated in this way. The drill bit is located at the lower end of the drill string, this drill bit having different cutting mechanisms, depending on the soil or type of rock, and being drawn out of the drill hole together with the drill bit at the end of the drilling operation. Controlled flushing of the drill bit and of the drill string is extremely important for a successful drilling operation. A pump delivers the flushing medium through the drill string, directly to the drill bit, where the drill cuttings removed are transported to the surface by way of the annular space produced between the drill string and drill-hole wall. This avoids any blockage of the drill hole. After filtering processes, the flushing medium can be returned into the circuit. In order to change the drill bit or to introduce and remove components which are guided at the bottom of the drill string, for example measuring instruments, drilling motors, core drills or the like, the entire drill string is removed and, once the corresponding components have been mounted at the lower end, introduced again. This operation of removing the entire drill string and introducing it again is referred to as a “round trip”.
Proceeding from the prior art mentioned, it is an object of the invention to develop a sampling technology and a sampling apparatus which make it possible to extract a sample while maintaining the environmental conditions prevailing at the sampling location—“in situ”—, the intention being to overcome the aforementioned disadvantages.
The sample-extracting process and the sampling apparatus should ensure not just that the environmental conditions prevailing at the sampling location are maintained, but also that an essentially intact sample, that is to say one which is not contaminated to any significant extent, is obtained.
In conjunction with the novel procedure in the novel two-stage “round-trip process”, which will be presented herein below, the following description of the invention also refers to the sampler according to the invention as a “round-trip autoclave sampler”. The “round-trip autoclave sampler” is suitable, in particular, for use within the novel round-trip process.
Use beyond the round-trip process, however, is not ruled out. Individual modules of the round-trip autoclave sampler may also be used, independently of the round-trip process, in other sampling processes or other autoclave samplers.